Polysilicon photodetector, methods and applications

ABSTRACT

A silicon photonic photodetector structure, a method for fabricating the silicon photonic photodetector structure and a method for operating a silicon photonic photodetector device that results from the photonic photodetector structure each use a strip waveguide optically coupled with a polysilicon material photodetector layer that may be contiguous with a semiconductor material slab to which is located and formed a pair of electrical contacts separated by the polysilicon material photodetector layer. Within the foregoing silicon photonic photodetector structure and related methods the polysilicon material photodetector layer includes defect states suitable for absorbing an optical signal from the strip waveguide and generating an electrical output signal using at least one of the electrical contacts when the optical signal includes a photon energy less than a band gap energy of a polysilicon material from which is comprised the polysilicon material photodetector layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to, and derives priority from, U.S.Provisional Patent Application Ser. No. 61/443,769, filed 17 Feb. 2011and titled “Photodiode in Deposited Silicon Apparatus, Method, andApplications,” the contents of which are incorporated herein fully byreference.

BACKGROUND

1. Field of the Invention

Embodiments relate generally to photodetector structures andphotodetector devices, such as but not limited to photodiode structuresand photodiode devices, within photonic circuits. More particularly,embodiments relate to integration of photodetector structures andphotodetector devices, such as but not limited to photodiode structuresand photodiode devices, with additional structures and additionaldevices within photonic circuits.

2. Description of the Related Art

The monocrystalline silicon-on-insulator (SOI) platform enables signalmodulation and low-loss waveguiding in the telecommunication wavelengthsignal bands centered at λ=1.3 μm and 1.55 μm. These modulation andwaveguiding functions can be implemented due to a 1.12 eV bandgap ofbulk monocrystalline Si, which only produces significant linearabsorption for λ<1.1 μm. To add infrared (IR) telecommunicationwavelength photodetection capabilities to silicon photonic circuits,other non-silicon materials typically must be added. Compoundsemiconductors such as indium phosphide-based materials may beheterogeneously integrated with silicon photonic circuits, butmore-desirable monolithic integration is limited due to materialrestrictions in complementary metal-oxide semiconductor (CMOS)processing environments. In contrast, germanium may be monolithicallyintegrated as an absorbing material in CMOS processing environments.However, epitaxial growth of Ge-on-Si requires complex processing stepsto manage a 4% lattice mismatch between a germanium crystal structureand a silicon crystal structure.

Given a continued interest in IR telecommunication wavelength signalphotodetection within silicon photonic circuits, desirable areadditional silicon photonic structures, silicon photonic devices andrelated methods that provide for IR telecommunication wavelengthphotodetection while providing for ready fabrication while usingconventional silicon photonic structure fabrication processes andconventional silicon photonic structure fabrication methodology.

SUMMARY

Embodiments include: (1) silicon photonic photodetector structures suchas but not limited to photodiode structures, compatible with a siliconphotonic circuit; (2) methods for fabricating the silicon photonicphotodetector structures, such as but not limited to the photodiodestructures, compatible with the silicon photonic circuit; and (3)methods for operating a silicon photonic photodetector device, such asbut not limited to a photodiode device, that results from the siliconphotonic photodetector structures. Within the context of the foregoingsilicon photonic photodetector structures and related methods a siliconphotonic photodetector structure comprises a strip waveguide located andformed over a substrate and optically coupled with a polysiliconmaterial photodetector layer (i.e., generally but not exclusively aphotodiode photodetector layer) also located and formed over thesubstrate. The polysilicon material photodetector layer may becontiguous with (i.e., at least electrically connected with, andpreferably formed from the same material layer as) a semiconductormaterial slab to which is located and formed a pair of electricalcontacts that is separated by the polysilicon material photodetectorlayer. Within the foregoing silicon photonic photodetector structure andrelated methods, the polysilicon material photodetector layer containsdefect states suitable for absorbing an optical input signal from thestrip waveguide and generating an electrical output signal using atleast one of the pair of electrical contacts, when the particularoptical input signal within the strip waveguide also contains a photonenergy less than the polysilicon material photodetector layer band gapenergy. In addition, the foregoing structures and methods may alsoinclude located and formed over the same substrate as the stripwaveguide, the polysilicon material photodetector layer and theelectrical contacts circuitry adapted to detect an electrical outputsignal using the at least one of the pair of electrical contacts whenintroducing an optical signal at the strip waveguide.

Within the silicon photonic photodiode structure in accordance with theembodiments, when an IR telecommunications wavelength signal (i.e.,which may be multiplexed) is introduced into the strip waveguide, aphotodiode (or alternate photodetector) photodetection signal (i.e.,which may be demultiplexed) may be measured using at least one of theelectrical contacts.

A method for fabricating a silicon photonic photodiode structure inaccordance with the embodiments may include specific structural featuresthat are included within the foregoing silicon photonic photodetectorstructure.

A method for operating a silicon photonic photodetector device thatresults from the silicon photonic photodetector structure in accordancewith the embodiments includes introducing the optical signal at thestrip waveguide while measuring a photodetection electrical signal usingat least one of the electrical contacts.

A silicon photonic photodetector structure in accordance with theembodiments, a method for fabricating the silicon photonic photodetectorstructure in accordance with the embodiments and a method for operatingthe silicon photonic photodetector device that derives from the siliconphotonic photodetector structure in accordance with the embodiments aredesirable insofar as the polysilicon material from which is comprisedthe silicon photonic photodetector structure is readily deposited usingdeposition processing that is otherwise generally conventional in thesilicon photonic circuit fabrication art, and thus germanium processesand germanium photodetector structures and devices (or other non-siliconmaterials, processes, structures and devices, such as but not limited toindium phosphide materials, processes, structures and devices) may beavoided.

Most broadly, embodiments of a silicon photonic structure, a method forfabricating the silicon photonic structure and a method for operating asilicon photonic device that derives from the silicon photonic structureinclude: (1) a strip waveguide located and formed over the substrate;(2) a polysilicon material photodetector layer also located and formedover the substrate and optically coupled with the strip waveguide; and(3) a pair of electrical contacts located and formed contactingseparated (i.e., normally by the strip waveguide) portions of thepolysilicon material photodetector layer. The silicon photonic structureand related methods also include at least one of: (1) the foregoingpolysilicon material photodetector layer defect states suitable forabsorbing an optical input signal from the strip waveguide andgenerating an electrical output signal using at least one of the pair ofelectrical contacts, when the particular optical input signal within thestrip waveguide also contains a photon energy less than the polysiliconmaterial photodetector layer band gap energy limitation, as describedabove; and (2) the foregoing circuitry adapted to detect an electricaloutput signal using the at least one of the pair of electrical contactswhen introducing an optical signal at the strip waveguide limitation, asalso described above.

Additional more specific embodiments are described as follows.

A particular photonic structure in accordance with the embodimentsincludes a strip waveguide located over a substrate. The particularphotonic structure also includes a polysilicon material photodetectorlayer also located over the substrate and optically coupled with thestrip waveguide. The polysilicon material photodetector layer iscontiguous with a semiconductor material slab also located over thesubstrate. The particular photonic structure also includes a pair ofelectrical contacts contacting portions of the semiconductor materialslab separated by the polysilicon material photodetector layer. Thepolysilicon material photodetector layer includes defect states suitablefor absorbing an optical signal from the strip waveguide and generatingan electrical output signal using at least one of the electricalcontacts when the optical signal includes a photon energy less than aband gap energy of a polysilicon material from which is comprised thepolysilicon material photodetector layer.

Another particular photonic structure in accordance with the embodimentsincludes a strip waveguide located over a substrate. This otherparticular photonic structure also includes a polysilicon materialphotodetector layer also located over the substrate and opticallycoupled with the strip waveguide. The polysilicon material photodetectorlayer is contiguous with a semiconductor material slab also located overthe substrate. This other particular photonic structure also includes apair of electrical contacts contacting portions of the semiconductormaterial slab separated by the polysilicon material photodetector layer.This other particular photonic structure also includes circuitry locatedover the substrate and connected to the pair of electrical contacts, andadapted to detect an electrical output signal using at least one of thepair of electrical contacts when introducing an optical signal at thestrip waveguide.

A particular method for fabricating a photonic device includes formingover a substrate a strip waveguide. The particular method also includesforming over the substrate a polysilicon material photodetector layercontiguous with a semiconductor material slab. The particular methodalso includes forming over the substrate and contacting portions of thesemiconductor material slab separated by the polysilicon materialphotodetector layer a pair of electrical contacts. The polysiliconmaterial photodetector layer is formed with defect states suitable forabsorbing an optical signal from the strip waveguide and generating anelectrical output signal using at least one of the electrical contactswhen the optical signal includes a photon energy less than a band gapenergy of a polysilicon material from which is comprised the polysiliconmaterial photodetector layer.

Another particular method for fabricating a photonic device includesforming over a substrate a strip waveguide. This other particular methodalso includes forming over the substrate a polysilicon materialphotodetector layer optically coupled with the strip waveguide andcontiguous with a semiconductor material slab also formed over thesubstrate. This other particular method also includes forming over thesubstrate and contacting portions of the semiconductor material slabseparated by the polysilicon material photodetector layer a pair ofelectrical contacts. This other particular method also includes formingover the substrate and connected to the pair of electrical contactscircuitry adapted to detect an electrical output signal using at leastone of the pair of electrical contacts when introducing an opticalsignal at the strip waveguide.

A particular method for operating a photonic device includes providing aphotonic structure including: (1) a strip waveguide located over asubstrate; (2) a polysilicon material photodetector layer also locatedover the substrate and optically coupled with the strip waveguide, thepolysilicon material photodetector layer contiguous with a semiconductormaterial slab also located over the substrate; and (3) a pair ofelectrical contacts contacting portions of the semiconductor materialslab separated by the polysilicon material photodetector layer, thepolysilicon material photodetector layer including defect statessuitable for absorbing an optical signal from the strip waveguide andgenerating an electrical output signal using at least one of theelectrical contacts when the optical signal includes a photon energyless than a band gap energy of a polysilicon material from which iscomprised the polysilicon material photodetector layer. The method alsoincludes introducing an optical signal into the strip waveguide, theoptical signal including the photon energy less than the bandgap of thepolysilicon material from which is comprised the polysilicon materialphotodetector layer. The method also includes measuring the electricaloutput signal while using the at least one of the electrical contacts.

Another particular method for operating a photonic device includesproviding a photonic structure comprising: (1) a strip waveguide locatedover a substrate; (2) a polysilicon material photodetector layer alsolocated over the substrate and optically coupled with the stripwaveguide, the polysilicon material photodetector layer contiguous witha semiconductor material slab also located over the substrate; (3) apair of electrical contacts contacting portions of the semiconductormaterial slab separated by the polysilicon material detector layer; and(4) circuitry adapted to detect an electrical output signal using atleast one of the pair of electrical contacts when introducing an opticalsignal at the strip waveguide. This other particular method alsoincludes introducing an optical signal into the strip waveguide. Thisother particular method also includes measuring the electrical outputsignal while using the at least one of the electrical contacts.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects, features and advantages of the embodiments are understoodwithin the context of the Detailed Description of the Embodiments, asset forth below. The Detailed Description of the Embodiments isunderstood within the context of the accompanying drawings, which form amaterial part of this disclosure, wherein:

FIG. 1 a and FIG. 1 b show, respectively, an optical microscopyplan-view image and a corresponding schematic cross-sectional diagram ofa silicon photonic photodiode structure in accordance with theembodiments.

FIG. 2 a to FIG. 2 i show a series of schematic cross-sectional diagramsillustrating the results of progressive stages in fabricating a siliconphotonic photodiode structure in accordance with the embodiments.

FIG. 3( a) shows a Transmission versus Wavelength and a Photocurrentversus Wavelength spectrum of a silicon photonic photodiode device inaccordance with the embodiments.

FIG. 3( b) shows a close scan at resonance spectrum of Photocurrentversus Wavelength and Responsivity versus Wavelength for a siliconphotonic photodiode device in accordance with the embodiments.

FIG. 3( c) shows Current versus Voltage characteristics under dark andlight conditions for a silicon photonic photodiode device in accordancewith the embodiments at various optical powers coupled into the siliconphotonic photodiode device.

FIG. 3( d) shows Responsivity versus Optical Power and Photocurrentversus Optical Power characteristics for a silicon photonic photodiodedevice in accordance with the embodiments.

FIG. 4( a) show a direct AC output Voltage versus Time spectrum of asilicon photonic photodiode device in accordance with the embodiments.

FIG. 4( b) shows an amplified electrical output eye diagram for asilicon photonic photodiode device in accordance with the embodiments.

FIG. 5( a) and FIG. 5( b) show, respectively, a schematicperspective-view diagram and a schematic cross-sectional diagram of asilicon photonic photodiode structure in accordance with a firstadditional embodiment.

FIG. 6( a) and FIG. 6( b) show, respectively, a schematicperspective-view diagram and a schematic cross-sectional diagram of asilicon photonic photodiode structure in accordance with a secondadditional embodiment.

FIG. 7( a) and FIG. 7( b) show, respectively, a schematicperspective-view diagram and a schematic cross-sectional diagram of asilicon photonic photodiode structure in accordance with a thirdadditional embodiment.

FIG. 8( a) and FIG. 8( b) show, respectively, a schematicperspective-view diagram and a schematic cross-sectional diagram of asilicon photonic photodiode structure in accordance with a fourthadditional embodiment.

FIG. 9( a) and FIG. 9( b) show, respectively, a schematicperspective-view diagram and a schematic cross-sectional diagram of asilicon photonic photodiode structure in accordance with a fifthadditional embodiment.

FIG. 10( a) and FIG. 10( b) show a pair of metallization schemes thatmay be used in fabricating a silicon photonic photodiode structure inaccordance with the embodiments.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments provide silicon photonic photodetector structures, methodsfor fabricating the silicon photonic photodetector structures andmethods for operating a silicon photonic photodetector device thatresults from the silicon photonic photodetector structures. Within thecontext of the foregoing silicon photonic photodetector structures,methods for fabricating the silicon photonic photodetector structuresand methods for operating the silicon photonic photodetector devicesthat result from the silicon photonic photodetector structures, there isemployed a strip waveguide located and formed over a substrate that isoptically coupled to a polysilicon material photodetector layer that isalso located and formed over the substrate. The polysilicon materialphotodetector layer may be located and formed contiguous with asemiconductor material slab to which is located and formed a pair ofelectrical contacts at positions separated by the polysilicon materialphotodetector layer. Within the foregoing embodiments, the polysiliconmaterial photodetector layer may be tuned for photodiode photodetectioncharacteristics by incorporation of a comparatively lightly doped dopantthat provides for a photodiode photodetection effect within thepolysilicon material photodetector layer.

While the embodiments illustrate a silicon photonic photodetectorstructure and related methods within the context of a silicon photonicphotodiode structure and related methods, the embodiments are notintended to be so limited, and to that end also may be included areother photodetector devices that may be formed from polysilicon materialphotodetector layers. Such other photodetector devices may include, butare not necessarily limited to, charge-coupled devices,phototransistors, and avalanche photodiodes.

Similarly, while the embodiments most commonly illustrate a siliconphotonic photodetector structure and related methods that include asemiconductor material slab for supporting a polysilicon materialphotodetector layer, this also is not intended to limit the embodiments.Rather, the embodiments also illustratively include an example where apolysilicon material photodetector layer is located and formed conformalto a strip waveguide which in turn is located and formed upon or over asubstrate absent a specifically denominated semiconductor material slab.In the presence of the semiconductor material slab, electrical contactsare commonly located and formed to the semiconductor material slab atlocations separated by the polysilicon material photodetector layer. Inthe absence of the semiconductor material slab, electrical contacts aretypically located and formed at locations of the polysilicon materialphotodetector layer separated by a strip waveguide.

1. Basic Structural Elements and Features of the Silicon PhotonicPhotodiode Structure

FIG. 1( a) and FIG. 1( b) show, respectively, an optical microscopyplan-view image and a corresponding schematic cross-sectional diagram ofa silicon photonic photodiode structure in accordance with theembodiments.

As is illustrated within the optical microscopy plan-view image of FIG.1( a), a silicon photonic photodiode structure in accordance with theembodiments includes a strip waveguide (i.e., at left hand side of FIG.1( a) and designated as “waveguide”) operatively optically coupled to apolysilicon material photodetector layer in the form of a ring waveguide(designated as “ring”) to the right of the strip waveguide and closer tothe center of the optical microscopy plan-view image of FIG. 1( a).Within the silicon photonic photodiode structure whose opticalmicroscopy image is illustrated in FIG. 1( a), the strip waveguide has alinewidth from about 300 to about 700 nanometers and a thickness fromabout 100 to about 600 nanometers. In addition, the ring waveguide has alinewidth from about 300 to about 2000 nanometers and a thickness fromabout 100 to about 600 nanometers, as well as a ring radius from greaterthan about 30 to about 70 microns, more preferably from about 40 toabout 60 microns and yet more preferably from about 45 to about 55microns.

The optical microscopy plan-view diagram of FIG. 1( a) also shows acomparatively heavily doped p+ region interior to and at least in partcoaxial with the ring waveguide, and a comparatively heavily doped n+region exterior to and at least in part coaxial with the ring waveguide.Further details regarding the foregoing p+ and n+ regions will bediscussed within the context of additional drawings that follow.

Finally, FIG. 1( a) shows: (1) at the upper and lower portions of theoptical microscopy plan-view image metal contact layers to thecomparatively heavily doped exterior n+ region; and (2) at the righthand side a generally larger metal contact (designated as “metal”) thatserves as a contact point to the comparatively heavily doped interior p+region.

FIG. 1( b) shows a schematic cross-sectional diagram illustrating thesilicon photonic photodiode structure whose optical microscopy plan-viewimage is illustrated in FIG. 1( a). The schematic cross-sectionaldiagram of FIG. 1( b) is taken through a cross-section that correspondswith the dashed line that includes the comparatively heavily doped p+region, the ring waveguide and the comparatively heavily doped n+ regionat the metal contact layer that is not otherwise designated at the topcentral portion within the silicon photonic photodiode structure whoseoptical microscopy plan-view image is illustrated in FIG. 1( a). As isillustrated within FIG. 1( b), and as will be discussed in furtherdetail below, a silicon photonic photodiode structure in accordance withthe embodiments includes as the ring waveguide a comparatively lightlydoped polysilicon material mesa (designated as “polysilicon n−”) that iscontiguous with (i.e., electrically contiguous with), extends from andrises above a semiconductor material slab which in general comprises thesame lightly doped polysilicon material as the lightly doped polysiliconmaterial mesa (i.e., generally but not exclusively n− at about 1E14 toless than about 1E18 dopant atoms per cubic centimeter). Thesemiconductor material slab further includes, separated by thecomparatively lightly doped polysilicon material mesa, a pair ofcomparatively heavily doped contact regions, one of the same includingan n+ dopant type and the other including a p+ dopant type. As isillustrated within the schematic cross-sectional diagram of FIG. 1( b),the silicon photonic photodiode structure is passivated with a siliconoxide material layer into which is formed apertures to accommodate aplurality of vias (i.e., electrical contacts) that contact thecomparatively heavily doped n+ and p+ regions, and to which vias arealso connected metallization layers that allow for a photodetectionoutput signal to be measured while using at least one of thecomparatively heavily doped p+ and n+ regions that comprise in-part asilicon photonic photodiode structure in accordance with theembodiments. Thus, the embodiments also are intended to include specificcircuitry that adapts the silicon photonic photodetector apparatus inaccordance with the embodiments to use as a photodetection apparatus(i.e., an optical absorption and electrical conversion apparatus) ratherthan alternative photonic apparatus.

Thus, in operation of a silicon photonic photodiode device that derivesfrom the silicon photonic photodiode structure in accordance with theembodiment as illustrated within the optical microscopy plan-viewdiagram of FIG. 1( a) and the schematic cross-sectional diagram of FIG.1( b), an optical signal is introduced into the strip waveguide and anelectrical photodetection output signal may be measured while using atleast one of the two comparatively highly doped p+ and n+ regions (oralternatively at electrical contacts located and formed connected to thecomparatively highly doped p+ and n+ regions).

Moreover, while the embodiments as illustrated within the opticalmicroscopy plan-view image of FIG. 1( a) and the schematiccross-sectional diagram of FIG. 1( b) illustrate the embodiments withinthe context of a strip waveguide optically coupled to a ring waveguidelocated and formed coplanar, such a relative disposition of the stripwaveguide and the ring waveguide is not intended to limit theembodiments. Rather, the strip waveguide (or an alternative geometricform waveguide that may alternatively be characterized and regarded as abus waveguide) may be located and formed in any of several geometricdispositions with respect to a ring waveguide in accordance with theembodiments provided that the strip waveguide (or alternative geometricform waveguide) and the ring waveguide are appropriately opticallycoupled, which within the context of IR telecommunications wavelengthdesirable within the context of the embodiments is a separation distancefrom about 100 to about 1000 nanometers, dependent on the refractiveindices of the materials in use. Thus, the embodiments also contemplatea silicon photonic photodetector structure where a strip waveguide and aring waveguide are coplanar or alternatively where a strip waveguide islocated and formed vertically separated either above or below a ringwaveguide.

Moreover, while the optical microscopy plan-view image of FIG. 1( a) andthe schematic cross-sectional diagram of FIG. 1( b) illustrate theembodiments within the context of a strip waveguide and a ring waveguideeach of which may comprise polysilicon, the embodiments are again alsonot intended to be so limited. Rather, while the embodiments contemplatethat the ring waveguide comprises a polysilicon material, thesemiconductor material slab with which the ring waveguide is contiguousand extends from, as well as the strip waveguide, may comprise othermaterials (i.e., such as but not limited to monocrystalline siliconmaterials, amorphous silicon materials, silicon nitride materials,silicon oxynitride materials and polymer materials) that may providegreater fidelity within the context of optical and electricalperformance of a silicon photonic photodiode device that results fromoperation of a silicon photonic photodiode structure in accordance withthe embodiments.

Finally, although the embodiments as illustrated within the opticalmicroscopy plan-view diagram of FIG. 1( a) and the schematiccross-sectional diagram of FIG. 1( b) illustrate a photonic structurethat includes a silicon photonic photodiode structure including a singlering waveguide, this particular photonic structure also is not intendedto limit the embodiments. Rather, the embodiments also contemplate thatmultiple ring waveguides of the same dimensions as described above maybe operatively coupled to a single strip waveguide.

In addition, the embodiments also contemplate that ring waveguides ofdifferent ring radii may also be coupled to the same or different stripwaveguides to provide photonic structures in accordance with theembodiments. In that regard, a silicon photonic structure in accordancewith the embodiments may include a silicon photonic ring resonatorstructure that provides a silicon photonic modulator structure, as wellas a silicon photonic photodiode structure. Such photonic ring resonatorstructures within the context of modulator structures are described ingreater detail in U.S. Patent Application Publication No. 2011/0293216,the content of which is incorporated herein fully by reference.

2. Fabrication Methodology for the Silicon Photonic Photodiode Structure

FIG. 2( a) to FIG. 2( j) show a series of schematic cross-sectionaldiagrams illustrating the results of progressive stages in fabricating asilicon photonic photodiode structure in accordance with theembodiments, as illustrated within the optical microscopy plan-viewdiagram of FIG. 1( a) and the schematic cross-sectional diagram of FIG.1( b). FIG. 2( a) shows a schematic cross-sectional diagram of thesilicon photonic photodiode structure at an early stage in thefabrication thereof in accordance with the embodiments.

FIG. 2( a) first shows a silicon substrate 10 having located and formedthereupon a buried oxide layer 12. Within the embodiments, the siliconsubstrate 10 and the buried oxide layer 12 may be otherwise generallyconventional in the silicon photonic structure fabrication art and theoptoelectronic structure fabrication art. Typically, the siliconsubstrate 10 comprises a silicon semiconductor material that may includeeither an n type dopant or a p type dopant, and any of several dopantconcentrations. Typically, the silicon substrate 10 may also includelocated and formed therein and/or thereupon semiconductor devices as areotherwise generally conventional, such semiconductor devices includingbut not limited to resistors, transistors, diodes and capacitors.

The buried oxide 12 may in general comprise any of several dielectricmaterials, such as but not limited to silicon oxide dielectricmaterials, silicon nitride dielectric materials and silicon oxynitridedielectric materials, but more specifically comprises a silicon oxidedielectric material when the silicon substrate 10 comprises a siliconsemiconductor material. Under such circumstances, the buried oxide layer12 may be formed using any of several methods, including but not limitedto thermal annealing methods, chemical vapor deposition methods andphysical vapor deposition methods. Typically, the buried oxide layer 12comprises a thermal silicon oxide dielectric material located and formedupon the silicon substrate 10 to a thickness from about 1 to about 5microns.

FIG. 2( b) shows the results of locating and forming an amorphoussilicon layer 14 upon the buried oxide layer 12 within the siliconphotonic photodiode structure of FIG. 2( a). The amorphous silicon layer14 may be located and formed upon the buried oxide layer 12 within thesilicon photonic photodiode structure whose schematic cross-sectionaldiagram is illustrated in FIG. 2( a) to provide the silicon photonicphotodiode structure whose schematic cross-sectional diagram isillustrated in FIG. 2( b) while using methods as are generallyconventional in the silicon photonic fabrication art and theoptoelectronic fabrication art. Typically, the amorphous silicon layer14 is located and formed upon the buried oxide layer 12 to a thicknessfrom about 100 to about 600 nanometers. While the amorphous siliconlayer 14 as illustrated within the schematic cross-sectional diagram ofFIG. 2( b) may be formed with a co-deposited dopant, the present processsequence does not particularly indicate or suggest that particular typeof process sequence. Generally, the amorphous silicon layer 14 may beformed using methods including but not limited to chemical vapordeposition methods and physical vapor deposition methods.

FIG. 2( c) shows the results of ion implanting the amorphous siliconlayer 14 that is illustrated within the schematic cross-sectionaldiagram of FIG. 2( b) with a dose of dopant ions 16 to form a dopedamorphous silicon layer 14′ from the amorphous silicon layer 14 that isillustrated in FIG. 2( b). While the doped amorphous silicon layer 14′may comprise either an n or p dopant, the doped amorphous silicon layer14′ is typically located and formed upon the buried oxide layer 12including an n-dopant (i.e., an arsenic or phosphorus dopant) to providea comparatively lightly doped n− volume concentration from about 1E14 toless than about 1E18 n-dopant atoms per cubic centimeter within thedoped amorphous silicon layer 14′.

FIG. 2( d) shows the results of thermally annealing the silicon photonicphotodiode structure of FIG. 2( c) to provide from the doped amorphoussilicon layer 14′ a doped polysilicon layer 14″. Such a dopedpolysilicon layer 14″ may be formed from the doped amorphous siliconlayer 14′ by thermal annealing at a temperature from about 1000 to about1200 degrees centigrade for a time period from about 300 to about 600minutes, in an inert atmosphere, such as but not limited to a nitrogenatmosphere.

FIG. 2( e) shows the results of patterning the doped polysilicon layer14″ within the schematic cross-sectional diagram of FIG. 2( d) to form adoped polysilicon layer 14′″ that comprises a mesa centered within,contiguous with and extending upward from a semiconductor material slabthat contacts the buried oxide layer 12. In order to form from the dopedpolysilicon layer 14″ within the schematic cross-sectional diagram ofFIG. 2( d) from the doped polysilicon layer 14′″ within the schematiccross-sectional diagram of FIG. 2( e), one will generally employ twophotolithographic process steps. One photolithographic process step willgenerally be needed to form the slab and another photolithographicprocess step will generally be needed to form the mesa which comprisesthe ring waveguide in accordance with the embodiment. Each of thephotolithographic process steps will generally also use a chlorinecontaining etchant gas composition. Within the schematic cross-sectionaldiagram of FIG. 2( e), the resulting mesa will thus have a linewidth ofthe ring waveguide, as described above, and a thickness to the top ofthe slab as also described above. In addition, the slab portions of thedoped polysilicon layer 14′″ will typically have a thickness from about30 to about 60 nanometers. A strip waveguide in accordance with FIG. 1(a) and FIG. 1( b) may also be located and formed over the substrate 10either simultaneously with, or separately from, the doped polysiliconlayer 14′″.

FIG. 2( f) shows the results of implanting n+ and p+ diode contactregions into portions of the contiguous polysilicon slab that areseparated by the mesa within the doped polysilicon layer 14′″ that isillustrated in FIG. 2( e) to in-turn provide a doped polysilicon layer14″″. In accordance with discussion above, each of the n+ and p+ moreheavily doped regions has a dopant concentration from greater than about1E18 to about 1E22 dopant atoms per cubic centimeter.

FIG. 2( g) in particular shows the results of encapsulating the siliconphotonic photodiode structure of FIG. 2( f) while using a silicon oxidematerial layer generally similar with the buried oxide layer 12 to forman encapsulating passivating layer 12′ that completely encapsulates thedoped polysilicon layer 14″″. Intended within the schematiccross-sectional diagram of FIG. 2( g) is a thickness of silicon oxidematerials about 3 microns below and about 1 micron above the dopedpolysilicon layer 14″″. This additional layer of silicon oxide materialmay be formed using methods including but not limited to chemical vapordeposition methods and physical vapor deposition methods. Typically, theadditional layer of silicon oxide material is formed using a plasmaenhanced chemical vapor deposition method. Also desirable in anannealing of the silicon photonic photodiode structure of FIG. 2( g)within an inert atmosphere such as but not limited to a nitrogenatmosphere under conditions such as but not limited to about 30 minutesat 600 degrees centigrade, 15 minutes at 900 degrees centigrade and 15seconds at 1050 degrees centigrade.

FIG. 2( h) shows the results of locating and forming a plurality ofapertures A through the passivating material layer 12′ and exposing thep+ and n+ contact regions within the doped polysilicon layer 14″″. Theforegoing apertures A may be formed using photolithographic and etchmethods as are otherwise generally conventional in the silicon photonicfabrication art, and in particular within the optoelectronic fabricationart.

Finally, FIG. 2( i) shows the results of locating and forming into theapertures A that are illustrated in FIG. 2( h) vias V which contact thep+ and n+ doped regions within the doped polysilicon layer 14″″, towhich vias V are located and formed metallization layers M, to thusprovide a finished silicon photonic photodiode structure in accordancewith the embodiments. Within the context of the schematiccross-sectional diagram of FIG. 2( i) often but not exclusively the viasV comprise a silicide material, such as but not limited to a nickelsilicide material, to provide a superior low contact resistanceconnection to the p+ and n+ doped regions located and formed within thedoped polysilicon layer 14″″. Typically, the vias V also comprisebarrier layers and conductor layers that are also generally otherwiseconventional, such as but not limited titanium, tantalum and tungstenmetal and metal nitride based barrier layers and conductor layers.Finally, the metallization layers M typically also include conductormaterials that are generally conventional, such conductor materialsbeing selected from the group including but not limited to aluminum,aluminum alloy, copper and copper alloy conductor materials.

3. Photodetection Characteristics of the Silicon Photonic PhotodiodeDevice

For accurate performance measurements of a silicon photonic photodiodedevice in accordance with the embodiments, the optical loss through asample and test setup must be carefully measured to determine accuratevalues of internal detector responsivity. Such measurements wereperformed by coupling light into a strip waveguide using a taperedlensed fiber and collecting the waveguide output with an objective lens.A polarization controller was used before the chip to select the TMpolarization, and a polarization filter was used after the chip. One maycalculate the waveguide propagation loss to be α_(wg)=34.6 dB/cm bylaunching light onto the chip from either direction as follows.Launching from the first facet, one may find the photocurrent onresonance to be I₁=RP_(in1)C_(in)(exp(−α_(wg)L₁))(1−T_(min)), andlaunching from the other facet one may we findI₂=RP_(in2)C_(in)(exp(−α_(wg)L₂))(1−T_(min)), where R is the internalresponsivity, P_(in1)(P_(in2)) is the power at the fiber tip for facet1(facet 2), C_(in) is the fiber-to-chip coupling efficiency, L₁(L₂) isthe propagation distance from facet 1(facet 2) to the device, T_(min) isthe on-resonance extinction ratio, and (1−T_(min)) is the fraction ofpower dropped into the ring. The equations reduce toI₁/I₂=P_(in1)exp(−α_(wg)L₁)/P_(in2)exp(−α_(wg)L₂), and one may solve forα_(wg)=34.6 dB/cm, which is primarily due to scattering but alsoincludes useful absorption. Then, by measuring the total chip insertionloss and subtracting the propagation loss, one may find the total chipcoupling loss (input facet plus output facet) to be 12.9 dB. One mayconservatively assume half of this coupling loss to be at the inputfacet. Additionally, there is 1.8 dB propagation loss from facet 1 tothe device, resulting in a total loss of 8.3 dB between the fiber tipand the device for the following measurements.

The internal responsivity of the silicon photonic photodiode device inaccordance with the embodiments was determined to be as high as 0.15A/W. FIG. 3( a) shows the transmission and measured photocurrent whenone sweeps the laser wavelength with a dc reverse bias on the siliconphotonic photodiode device. When light is on resonance and trapped inthe ring waveguide portion of the silicon photonic photodiode device, iteither scatters away or it is absorbed and generates photocurrent. FIG.3( b) shows the resonant photocurrent at −13 V. The optical power in thestrip waveguide (i.e., bus waveguide) at the device is P_(wg)=7.35 μW,and the transmission extinction ratio is (1−T_(min))×100%=90.5%, soP_(det)=(1−T_(min))×P_(wg)=6.65 μW is coupled into the resonator.Observed was a quality factor Q=10,500 and a maximum photocurrentI=0.975 μA corresponding to internal responsivity R=0.15 A/W. Themicro-ring waveguide silicon photonic photodiode device acts as awavelength-selective photodetector, which can both de-multiplex andphotodetect one wavelength of a WDM signal. This combined functionalityis not possible in strongly absorbing materials where high loss wouldprevent the formation of a high-Q resonance.

The responsivity of the silicon photonic photodiode device wasdetermined by the efficiency of both carrier generation (given by theratio of absorption loss to total propagation loss in polysilicon) andcarrier extraction. The absorption may be considered to be due todangling bonds, which produce a distribution of trap states slightlybelow the midbandgap energy, many of which are filled by donorelectrons. It is likely that, in the silicon photonic photodiode devicein accordance with the embodiments, the photocarrier generation isprimarily due to the n− phosphorus donor electrons being promoted fromthese trap states to a conduction band.

Also measured for the silicon photonic photodiode device in accordancewith the embodiments was a low dark current of 40 nA at an operatingvoltage of −13 V. FIG. 3( c) shows current-voltage curves with andwithout light coupled to the silicon photonic photodiode device with thewavelength on resonance. The photocurrent does not plateau but rathercontinues increasing with reverse bias voltage. This effect can likelybe improved by placing contacts closer to where the carriers aregenerated or by tailoring the dopant concentration to ensure fulldepletion of the waveguide region. It was observed that the siliconphotonic photodiode device in accordance with the embodiments was notoperating in an avalanche regime, which would otherwise produce arapidly increasing dark current for V<−14 V. FIG. 3( d) showsresponsivity as a function of the optical power coupled into the siliconphotonic photodiode device at a bias voltage of −13 V. One may observethat the internal responsivity decreases from 0.15 A/W to 0.10 A/W asthe optical power is increased over nearly 2 orders of magnitude. Thisdecrease presumably indicates that either the generation or extractionof carriers is suppressed at higher photocarrier densities in thesilicon photonic photodiode device and that these effects are largerthan any two-photon absorption effect, which would otherwise increasethe responsivity.

The transient response of the silicon photonic photodiode device wasalso measured by modulating a cw laser with an external modulator. FIG.4( a) shows the direct output of the silicon photonic photodiode deviceoperating at a bit rate of 2.5 Gbps. To obtain an eye diagram, thesilicon photonic photodiode device output was amplified with a low-noiseamplifier with 1 GHz bandwidth. An open eye diagram a 1 Gbps is shown inFIG. 4( b). The silicon photonic photodiode device S11 response wasmeasured using an HP8722ES vector network analyzer and the speed of therelatively large device was RC-limited. A circuit model and parameterfit was used to de-embed the parasitic contribution of contact pads, andthe junction capacitance was observed to be 100 fF+/−7 fF and seriesresistance was observed to be 524Ω+/−25Ω. From those values, one maydetermine the electrical bandwidth of the silicon photonic photodiodedevice and pads terminated into a 50Ω load to be 2.6+/−0.24 GHz, whichcan be improved by engineering the device structure, reducing the sizeof the resonator, or integrating directly with a transimpedanceamplifier.

The absorption coefficient α_(abs) was calculated to be >=6 dB/cm insidethe device. The use of a near critically coupled resonator photodiode isequivalent to a long waveguide photodiode; photons in the cavity that donot scatter away must be absorbed. The measured quantum efficiencyQE=12% (for R=0.15 A/W at λ=1.55 μm) is therefore a lower bound forα_(abs)/α_(ring), the percent of propagation loss in the ring which isdue to absorption. From the Q and extinction ratio, one may calculatethe total propagation loss in the ring waveguide (absorption andscattering) to be α_(ring)=51.7 dB/cm, and the absorption coefficient istherefore α_(abs)>/=6.2 dB/cm. One may consider that the actualabsorption value is higher by the percentage of carriers that recombinebefore being extracted to the external circuit. Additionally, anidentical photodiode integrated into a straight waveguide instead of aresonator could have a maximum QE=α_(abs)/α_(wg)=(6.2 dB/cm)/(34.6dB/cm)=18%, based on the measured straight waveguide loss. Theresponsivity can be enhanced by optimizing the background dopant typeand concentration.

4. Alternative Embodiments

While the silicon photonic photodiode structure as described abovewithin the context of a strip waveguide and an optically coupled ringwaveguide is illustrative as an embodiment, such a silicon photonicphotodiode structure is nonetheless also not limiting of theembodiments. In that regard, FIG. 5 a and FIG. 5 b, FIG. 6 a and FIG. 6b, FIG. 7 a and FIG. 7 b, FIG. 8 a and FIG. 8 b, and FIG. 9 a and FIG. 9b show a series of schematic perspective-view diagrams and correspondingschematic cross-sectional view diagrams illustrating additional siliconphotonic photodiode structure embodiments.

For example, FIG. 5 a and FIG. 5 b show, respectively, a schematicperspective-view diagram and a schematic cross-sectional view diagram ofa silicon photonic photodiode structure in accordance with a firstadditional embodiment.

FIG. 5 a in a first instance shows a planar optical waveguide which isintended as illustrative of the strip waveguide that is illustrated inFIG. 1 a. FIG. 5 a also shows a polysilicon detector layer which islocated and formed upon a semiconductor material slab, upon whichsemiconductor material slab is also located and formed lateral electrodecontacts that are separated by the polysilicon detector layer.

FIG. 5 b shows a schematic cross-sectional diagram corresponding withthe silicon photonic photodiode structure whose schematicperspective-view diagram is illustrated in FIG. 5 a.

FIG. 5 b shows a substrate having located and formed thereupon a buriedoxide layer in turn having located and formed thereupon thesemiconductor material slab upon which is located and formed thepolysilicon detector layer that separates the lateral electrodecontacts. FIG. 5 b finally illustrates the planar optical waveguideoptically coupled to the polysilicon detector layer.

FIG. 6 a and FIG. 6 b show a schematic perspective-view diagram and aschematic cross-sectional view diagram that otherwise relate to theschematic perspective-view diagram and schematic cross-sectional diagramof FIG. 5 a and FIG. 5 b, but wherein the polysilicon detector layerfurther comprises apertures or holes. Due to the presence of suchapertures or holes, the polysilicon detector layer functions as aphotonic crystal which enhances the photodetection properties of thepolysilicon detector layer.

FIG. 7 a and FIG. 7 b show a schematic perspective-view diagram and aschematic cross-sectional view diagram of a silicon photonicphotodetector structure in accordance with yet another embodiment.

FIG. 7 a shows a schematic perspective-view diagram of a siliconphotonic photodiode structure similar in a first instance with thesilicon photonic photodiode structure in accordance with FIG. 1 a andFIG. 1 b, but wherein the planar optical waveguide that corresponds withthe strip waveguide that is illustrated in FIG. 1 a is in fact locatedand formed above or over the polysilicon detector layer rather thanlaterally separated from the polysilicon detector layer.

The schematic cross-sectional diagram of FIG. 7 b corresponds generally,if not necessarily exactly, with the schematic cross-sectional diagramof FIG. 6 b or the schematic cross-sectional diagram of FIG. 5 b.

FIG. 8 a and FIG. 8 b show a schematic perspective-view diagram and aschematic cross-sectional diagram of a silicon photonic photodetectorstructure in accordance with yet another embodiment.

FIG. 8 a and FIG. 8 b show a schematic perspective-view diagram and aschematic cross-sectional diagram of a silicon photonic photodetectorstructure analogous with the silicon photonic photodetector structurewhose schematic perspective-view diagram and cross-sectional viewdiagrams are illustrated in FIG. 5 a and FIG. 5 b, but wherein theplanar optical waveguide and the polysilicon detector layer are buttconnected as a form of optical coupling rather than, for example andwithout limitation, separated and evanescently optically coupled.

FIG. 9 a and FIG. 9 b show a schematic perspective-view diagram and aschematic cross-sectional diagram of a silicon photonic photodetectorstructure in accordance with yet another embodiment.

FIG. 9 a and FIG. 9 b relate generally to FIG. 8 a and FIG. 8 b, butwherein the polysilicon detector layer is formed nominally conformal tothe planar optical waveguide. Under these circumstances, alternatesub-embodiments exist which may or may not include a dielectric layerinterposed between the planar optical waveguide and the polysilicondetector layer. As well, while the slab portions of the semiconductormaterial slab still exist, they are now connected to form an n shapedcross-section polysilicon detector layer rather than a rectangularcross-sectioned polysilicon detector layer.

FIG. 10 a and FIG. 10 b show a pair of metallization structures that mayalso be used for forming a silicon photonic photodiode structure inaccordance with the embodiments.

Illustrated in FIG. 10 a is a metal-semiconductor-metal (MSM) structurethat uses a lightly doped polysilicon central portion which is contactedor capped at each end with a metal (i.e., which may be the same metal).The metal and the lightly doped semiconductor materials may be the sameas the metals and the lightly doped semiconductor materials that isdiscussed above within the context of the particular described firstembodiment.

In contrast, FIG. 10 b shows a metallization structure that includes alightly doped polysilicon central portion to which is laminated heavilydoped polysilicon material layers of a first type and a second type, towhich in turn is laminated metal lateral layers. As is understood by aperson skilled in the art, FIG. 10 b differs from FIG. 10 a by thepresence of the heavily doped polysilicon materials layers of the firsttype and of the second type. Thus, within the context of FIG. 10 a asilicon photonic polysilicon photodiode structure in accordance with theembodiments may include solely a metal-doped silicon-metal structure.

Common to all embodiments is thus a lightly doped polysilicon materiallayer as a photodiode photodetector material layer within a siliconphotonic photodiode structure. The embodiments contemplate thatmetallization electrical contacts may be formed directly to the lightlydoped polysilicon material, as well as to more highly doped polysiliconmaterial layers or polysilicon material regions.

The silicon photonic polysilicon photodetector structure presented herecan be integrated with CMOS SOI optical components for opticalinterconnect applications. However, these results also open the door toan integrated optical link which does not require any crystalline SOImaterial, but utilizes only silicon-based materials deposited in theCMOS stack. Desirably, both a modulator and a photodetector can befabricated from the same polysilicon material. Absorption can presumablybe suppressed in the modulator regions by hydrogen passivation andenhanced in the detector regions by optimizing the dopant type andconcentration. Additionally, propagation loss in deposited siliconnitride has been demonstrated as low as 0.1 dB/cm, approximately 20times better than losses in single-mode submicrometer crystalline SOIwaveguides. Because of the ultralow optical loss, it may be possible todesign optical links or networks whose system-level characteristicsoutperform the traditional SOI platform, even with some degradation inmodulator and detector device performance as compared to SOI andcrystalline Ge-on-Si.

In conclusion, demonstrated is an integrated silicon photonic photodiodestructure, method and device in polysilicon, a deposited CMOS material.The polysilicon exhibits 6 dB/cm absorption, which results in aresponsivity of 0.15 A/W. Demonstrated was 2.5 Gbps operation of thedevice and suggested was several areas of research for achieving deviceswith even higher performance.

All references, including publications, patent applications, and patentscited herein are hereby incorporated by reference in their entireties tothe same extent as if each reference was individually and specificallyindicated to be incorporated by reference and was set forth in itsentirety herein.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) is to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. The term “connected” is to beconstrued as partly or wholly contained within, attached to, or joinedtogether, even if there is something intervening.

The recitation of ranges of values herein is merely intended to serve asa shorthand method of referring individually to each separate valuefalling within the range, unless otherwise indicated herein, and eachseparate value is incorporated into the specification as if it wasindividually recited herein.

All methods described herein can be performed in any suitable orderunless otherwise indicated herein or otherwise clearly contradicted bycontext. The use of any and all examples, or exemplary language (e.g.,“such as”) provided herein, is intended merely to better illuminateembodiments of the invention and does not impose a limitation on thescope of the invention unless otherwise claimed.

No language in the specification should be construed as indicating anynon-claimed element as essential to the practice of the invention.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the present inventionwithout departing from the spirit and scope of the invention. There isno intention to limit the invention to the specific form or formsdisclosed, but on the contrary, the intention is to cover allmodifications, alternative constructions, and equivalents falling withinthe spirit and scope of the invention, as defined in the appendedclaims. Thus, it is intended that the present invention cover themodifications and variations of this invention provided they come withinthe scope of the appended claims and their equivalents.

What is claimed is:
 1. A photonic structure comprising: a stripwaveguide located over a substrate; a polysilicon material photodetectorlayer also located over the substrate and optically coupled with thestrip waveguide, the polysilicon material photodetector layer contiguouswith a semiconductor material slab also located over the substrate, thepolysilicon material photodetector layer and the semiconductor materialslab being formed of the same polysilicon material; and a pair ofelectrical contacts contacting a pair of doped semiconductor regionslocated within separated portions of the polysilicon materialphotodetector layer, wherein: the semiconductor material slab and thepolysilicon material photodetector layer have a dopant concentrationfrom about 1e14 to less than about 1e18 dopant atoms per cubiccentimeter; one of the pair of doped semiconductor regions comprises ap+ dopant at a concentration from greater than about 1E18 to about 1E22dopant atoms per cubic centimeter; and the other of the pair of dopedsemiconductor regions comprises an n+ dopant at a concentration fromgreater than about 1E18 to about 1E22 dopant atoms per cubic centimeter.2. The photonic structure of claim 1 wherein the polysilicon materialphotodetector layer comprises a planar polysilicon photodetector layer.3. The photonic structure of claim 1 wherein the strip waveguide islaterally separated from the polysilicon material photodetector layer.4. The photonic structure of claim 1 wherein the strip waveguide isvertically separated from the polysilicon material photodetector layer.5. The photonic structure of claim 1 wherein the polysilicon materialdetector layer does not include germanium.
 6. The photonic structure ofclaim 1 wherein the polysilicon material photodetector layer includesdefect states suitable for absorbing an optical signal from the stripwaveguide and generating an electrical output signal using at least oneof the electrical contacts when the optical signal includes a photonenergy less than a band gap energy of a polysilicon material from whichis comprised the polysilicon material photodetector layer.
 7. A photonicstructure comprising: a strip waveguide located over a substrate; apolysilicon material photodetector layer also located over the substrateand optically coupled with the strip waveguide, the polysilicon materialphotodetector layer contiguous with a semiconductor material slab alsolocated over the substrate, the polysilicon material photodetector layerand the semiconductor material slab being formed of the same polysiliconmaterial, the polysilicon material photodetector layer comprising aphotonic crystal resonator polysilicon photodetector layer; and a pairof electrical contacts contacting separated portions of the polysiliconmaterial photodetector layer.